Empty fuel level detection cross-check

Abstract

A fuel level monitoring system for a fuel system having a primary fuel tank and a secondary fuel tank includes a fuel level sensor that is disposed within the secondary fuel tank and that generates a first signal. An empty switch is disposed within the secondary fuel tank and generates a second signal. A control module determines a condition of one of the fuel level sensor and the empty switch based on the first signal, the second signal and a plurality of signal thresholds.

1. A fuel level monitoring system for a fuel system having a primary fuel tank and a secondary fuel tank, comprising:
 a fuel level sensor that is disposed within said secondary fuel tank and that generates a first signal; 
 an empty switch that is disposed within said secondary fuel tank, that is connected in series with said fuel level sensor, and that generates a second signal, wherein said fuel level sensor outputs a third signal corresponding to a sum of said first and second signals; and 
 a control module that determines a condition of one of said fuel level sensor and said empty switch based on comparisons of said third signal and each of a plurality of signal thresholds, wherein said condition includes at least one of a fuel level sensor stuck condition and an empty switch stuck condition. 
 
     
     
       2. The fuel level monitoring system of  claim 1  wherein said control module sets a condition flag based on said condition. 
     
     
       3. The fuel level monitoring system of  claim 2  wherein said condition flag indicates one of a fuel tank empty condition, a fuel tank full condition, a normal operating condition, an empty switch stuck condition and a fuel level sensor stuck condition. 
     
     
       4. The fuel level monitoring system of  claim 3  wherein said control module generates a diagnostic trouble code and initiates an alert when said condition is one of an empty switch stuck condition and a fuel level sensor stuck condition. 
     
     
       5. The fuel level monitoring system of  claim 1  wherein said first signal includes one of a first value, a second value and a third value. 
     
     
       6. The fuel level monitoring system of  claim 1  wherein said fuel level sensor is a variable resistor. 
     
     
       7. The fuel level monitoring system of  claim 1  wherein said second signal includes one of a first and a second value. 
     
     
       8. A method of evaluating whether a fuel monitoring apparatus is functioning properly, comprising:
 generating a first signal using a fuel level sensor disposed within a fuel tank; 
 generating a second signal using an empty switch disposed within said fuel tank; 
 determining a condition of one of said fuel level sensor and said empty switch based on said first signal, said second signal and a plurality of signal thresholds; and 
 adding said first and second signals; 
 wherein a resultant sum of said first and second signals is compared to each of said plurality of signal thresholds. 
 
     
     
       9. The method of  claim 8  further comprising setting a condition flag based on said condition. 
     
     
       10. The method of  claim 9  wherein said condition flag indicates one of a fuel tank empty condition, a fuel tank full condition, a normal operating condition, an empty switch stuck condition and a fuel level sensor stuck condition. 
     
     
       11. The method of  claim 8  wherein said first signal includes one of a first value, a second value and a third value. 
     
     
       12. The method of  claim 8  wherein said fuel level sensor is a variable resistor. 
     
     
       13. The method of  claim 12  wherein said empty switch is connected in electrical series with said fuel level sensor. 
     
     
       14. The method of  claim 8  wherein said second signal includes one of a first and a second value. 
     
     
       15. The method of  claim 8  wherein said first and second signals are resistances respectively associated with said fuel level sensor and said empty switch. 
     
     
       16. A method of evaluating whether a fuel monitoring sensor is functioning properly, comprising:
 providing a fuel system having first and second fuel tanks; 
 generating a first signal using a fuel level sensor disposed within said secondary fuel tank; 
 generating a second signal using an empty switch disposed within said secondary fuel tank; 
 determining a condition of one of said fuel level sensor and said empty switch based on said first signal, said second signal and a plurality of signal thresholds; and 
 adding said first and second signals, wherein a resultant sum of said first and second signals is compared to each of said plurality of signal thresholds. 
 
     
     
       17. The method of  claim 16  further comprising setting a condition flag based on said condition. 
     
     
       18. The method of  claim 17  wherein said condition flag indicates one of a fuel tank empty condition, a fuel tank full condition, a normal operating condition, an empty switch stuck condition and a fuel level sensor stuck condition. 
     
     
       19. The method of  claim 16  wherein said first signal includes one of a first value, a second value and a third value. 
     
     
       20. The method of  claim 16  wherein said fuel level sensor is a variable resistor. 
     
     
       21. The method of  claim 20  wherein said empty switch is connected in electrical series with said fuel level sensor. 
     
     
       22. The method of  claim 16  wherein said second signal includes one of a first and a second value. 
     
     
       23. The method of  claim 16  wherein said first and second signals are resistances respectively associated with said fuel level sensor and said empty switch.